Casings most commonly used for manufacturing frankfurters and the like comprise relatively long thin-walled tubes of regenerated cellulose. These tubes are made by extruding and then coagulating a viscose solution. For convenience of handling, the casings, which may be 20 to 70 meters or more in length, are shirred and compressed to produce what are commonly referred to in the art as "shirred casing sticks". A shirred stick which measures about 20 to 70 centimeters in length may contain upwards of 70 meters or more of casing.
Each shirred stick has an axial bore open at one end (usually the last shirred end of the stick) so the stick can be loaded onto a stuffing horn. The opposite end of the bore is closed to prevent loss of food emulsion which is extruded from the horn and into the casing. Processes for manufacturing cellulosic casings and for subsequently shirring them to produce the shirred sticks are well known in the art and will only be described herein in sufficient detail to facilitate an understanding of the present invention.
During the course of manufacturing a shirred stick, cellulosic casing from a reel or other supply is inflated and fed onto a mandrel. A shirring device gathers the casing into generally conical pleats nested one within another wherein the innerfold of each pleat is formed against the mandrel. When a desired shirred length has accumulated on the mandrel, the shirred stick is severed from the unshirred casing and is moved away from the shirring device. Subsequent operations are performed on the shirred stick while a new stick is being shirred.
For example, in one subsequent operation the shirred stick is longitudinally compacted to further reduce its length. In another operation, one end of the stick bore is closed.
Severing the shirred stick produces a "tail" of casing at the last-shirred end of the stick. During compaction this tail is longitudinally pressed against the pleats at the last-shirred end of the stick. The tail, compacted in this fashion, produces a ring of compressed casing which may disassociate or loosen from the end of the stick. This not only detracts from the appearance of the stick but also interferes with its utility by impeding the entry of a stuffing horn into and through the bore. A loose ring of compacted casing at the bore opening may become entangled or jammed about the horn. This in turn is likely to result in a casing break either during horn insertion or during stuffing. When such a break occurs, the stuffing machine must be shut down to clear the jam and to clean the stuffing machine of food emulsion which has spilled from the casing break. Due to these potential problems, a shirred stick having a loose ring of compacted casing at its open end generally is not satisfactory for use on high speed stuffing machines wherein shirred sticks are handled mechanically and are loaded automatically on the stuffing horn.
Various methods have been employed to prevent or eliminate a loose ring of compacted casing at the open end of the stick. In one conventional method, the shirring machine operator manually peels the loose ring of casing from the stick until only tightly nested pleats of shirred casing remain at the open end of the shirred stick. This method is labor intensive and not desirable.
The prevention or elimination of loose casing at the open end of the stick also is the subject of several U.S. Patents. For example, U.S. Pat. No. 3,544,339 discloses applying a thin wax coating to the pleats at the open end of the stick. This provides a wax cap which retains the integrity of the open end. U.S. Pat. No. 3,878,978 discloses a severing method including directing a stream of cold gas at the casing to render it so brittle that it severs without the formation of a tail.
U.S. Pat. No. 4,307,488 discloses a method of reforming the torn or severed last-shirred end of the stick by smoothing it during the longitudinal compacting operation. This is accomplished by closing two halves of a split frustro-conical member about the mandrel and pressing it against the last-shirred end of the stick. The member is then oscillated or rotated around the mandrel while the member longitudinally compacts the stick. The mandrel prevents entry of the member into the bore of the stick so it is not possible to smooth the bore surface adjacent the last-shirred end of the stick. Also, if the two halves do not fit tightly together, the non-mating edges of the two halves can abrade the end of the stick.
U.S. Pat. Nos. 4,594,274 and 4,624,873 disclose pressing a heated die against the end of the stick to iron loose casing against the tightly nested pleats at the open end by combination of heat and pressure. This requires temperature control to avoid excessive heating which can damage the stick end. Also, the operator must take care to avoid touching the hot die.